Hello,
I have a Casio MT-400V that was donated to me some time ago. All of the wiring had been desoldered by a previous owner!! I have no idea why. I have all the wiring and attempted to rebuild the whole unit but there are just too many unknown connections. Did the service manual help you out at all? I have unrelated casio service manuals as mentioned in this thread but I doubt that would be sufficient to rewire everything. I would like, to ask if you would be willing to document, photograph or record your repair the boards and wiring as you attempt to repair your unit? I did get some helpful info from watching You Tubes Keen On Keys video of the MT-400V and MT-410.
